There has long been a need for a wound dressing which is soft, pliable and elastic, yet high in tensile strength and abrasion resistance and which can release drugs at a controlled, sustained level.
Presently available bandages made of materials such as cotton are undesirable because they retain water, serve as growth mediums for bacteria, and soak up tissue pieces and blood which clots, causing adhesion to the wound and trauma during removal.
Other bandages are made with plastic coverings with an adhesion coating to decrease the undesirable water absorption of cotton wound dressings. Unfortunately, new problems were created due to lack of oxygen transmission through the plastic coating. Indeed, holes had to be punched through the plastic covering to allow the transmission of some oxygen to the skin below. Hard plastic or silicone coatings were also applied to the side of the bandage adjacent to the wound to prevent adhesion. These coatings did not significantly decrease the problem of the bandage sticking to the wound, and blocked oxygen and water transmission.
In further attempts to overcome the adhesion and permeability problems, polyurethane and other plastic dressings were tried. For example, U.S. Pat. No. 3,975,567 to Lock discloses a pressure and heat-treated polyurethane foam which is lyophilic.
Other polyurethanes which polymerize upon exposure to ultraviolet light were also developed. The majority of these UV-curable polyurethanes were designed for use as orthopedic casts, e.g., U.S. Pat. No. 4,209,605. Other types of polymers have been used as matrices for incorporation of biologically active agents and, in the form of polymerized sheets or films, have been used as wound dressings, such as the compounds disclosed by U.S. Pat. Nos. 4,321,117 (acrylic polymers) and 4,156,067 (polyurethane). None of these compositions managed to combine the properties of softness, oxygen and water vapor permeability, flexibility, thixotropy and capability for incorporation of biologically active agents, with a fast cure at room temperature to a tough, colorless film. The ability to cure at room temperature without release of heat is particularly important because many drugs are heat labile.
At present, the most commercially successful burn and superficial skin wound dressing is a polyether-based polyurethane, moisture-vapor permeable membrane compounded with silica gel. The composition, known as "Op-Site".RTM., described in U.S. Pat. Nos. 4,340,043 and 4,460,369 assigned to Smith & Nephew Research Ltd., is in the form of a thin film having a surface coated with a polyvinylethylether adhesive. Although considerably more comfortable, permeable, and effective as protection against bacterial contamination than the prior art wound dressings, this material still suffers from the inability to incorporate biologically active agents such as coagulants and antibiotics into the membrane, rather than into the adhesive, and from difficulty in formation and application as a bandage which conforms to the contour of the site of application. In connection with this latter problem, two to three people are required for application.
It is therefore an object of the present invention to provide a wound dressing which physically incorporates drugs such as antibiotics, coagulants, and anti-inflammatories into the dressing structure having appreciable tensile strength rather than into the adhesive or thin coating on the dressing so that the drugs are released in a controlled, sustained manner.
It is a further object of the present invention to provide a material for use as a wound dressing which is strong yet flexible, and which can be made to conform to the shape of the site of the wound.
It is a still further object of the present invention to provide such a material for use as a wound dressing which is nontoxic, non-carcinogenic, and biocompatible.
It is a further object of the present invention to provide a material which can be easily formed and applied to a wound by one person in adverse circumstances.
Yet a further object of the invention is to provide a polymeric material which is a liquid at room temperature and which has a sufficiently low viscosity at room temperature (prior to cure) to facilitate admixture with a drug to form a homogeneous blend.
Still a further object is to provide such a polymeric material which cures at room temperature without release of heat (non-exothermic).
The foregoing and other objects and features of the claimed invention will be understood by those skilled in the art from a reading of the description which follows.